Hydroxyalkyloxamide esters of 3-(3,5-dialkyl-4-hydroxyphenyl)propionic acid are excellent stabilizers and antioxidants for a variety of organic materials. They are described in U.S. Pat. No. 4,145,556 and in the inventor's copending applications, Ser. No. 043,790, entitled "N,N.sup.1 -Bis-2-3-(3,5-di-tert.-butyl-4-hydroxyphenyl)propionyloxy ethyl oxamide", Ser. No. 043,914, now abandoned, entitled "Phenolic Oxamide Antioxidants", and Ser. No. 043,761, entitled "Polyfunctional Phenolic Oxamide Antioxidants", assigned to Uniroyal, Inc., filed on even date herewith, the disclosures of which are hereby incorporated by reference: These esters can be made by the usual esterification or transesterification methods. The use of tin type transesterification catalysts is of particular value in making esters of 3-(3,5-di-alkyl-4-hydroxyplenyl)propionic acid. Strong acid catalysts tend to remove some of the tertiary alkyl groups from the phenolic ring during the transesterification. Strong bases tend to split the propionate into di-alkyl phenol and an acrylate. Tin catalysts are not known to promote either of these side reactions. They also have the advantage of being useful at very low concentrations (0.1-0.25%). A variety of tin transesterification catalysts are commercially available. The literature teaches that temperatures around 220.degree. C. are needed for a satisfactory rate. This presents a drawback in their use as many esters can decompose at that temperature.
It has surprisingly been found that in the case of transesterification with lower alkyl 3-(3,5-di-alkyl-4-hydroxyphenyl)propionates, using certain tin transesterification catalysts, the transesterification begins to take place at temperatures as low as 150.degree. C.